The present invention provides a method and apparatus for attaching a die plate to a cylinder segment which forms a side of a nip in which material is cut or creased. In particular the present invention provides a method and apparatus for attaching such a die plate to a cylinder segment in a manner which assures proper registration between two die plate attached in such a manner to two cylinder segments.
In a known cutting and creasing machine, material may be rupture cut or creased when it passes through a nip formed between a cooperating pair of die plates. Such a machine is shown in U.S. patent application Ser. No. 760,663, entitled "Cutting Apparatus" by Albert J. Sarka, filed Jan. 19, 1977. In this machine each die plate is attached in a fixed position to a semicircular cylinder segment which in turn is attached to a rotatable arbor.
Two such cylinder segments with die plates attached are connected with a pair of arbors to form a nearly continuous cylindrical die on each arbor. The arbors, and hence the cylinder segments and die plates, are rotated in opposite directions and material advanced through the nip between them is cut or creased. A known advantage of utilizing die plates which are attached to cylinder segments is that the die plates may be formed to provide a continuous cut or crease around a circumference of the die plates. This in turn enables such die plates to form a continuous cut along the length of a web of material.
Accurate registration between the lands on cooperating die plates is essential to proper cutting and creasing. In the past, circumferential registration of cooperating die plates with each other has been accomplished by moving one of the cylinder segments and the attached die plate circumferentially with respect to the arbor on which it is mounted.
The problem of accurate registration of cooperating plates is an old one, both in the printing art and in the cutting and creasing art. Plate cylinders for use in printing presses have been provided with axially extending gaps in which are disposed clamps which engage opposite ends of a printing plate. Registration is accomplished by moving the clamps circumferentially or axially until proper registration is achieved. The printing plates may also be provided with accurately located holes, and, in that case the adjustable clamps in the plate cylinder have corresponding pins to further assist in accurate registration. However, the gap required in a cylinder for plate clamps precludes the use of known registration techniques if a continuous cut is to be made.
It is also known to provide a fixed clamp on the plate cylinder to hold the printing plate fixed with respect to the plate cylinder. Registration is then achieved by mounting the cylinder so that it may be moved axially and/or circumferentially with respect to a cooperating cylinder.
However, difficulties have persisted in achieving proper registration especially when one plate is skewed with respect to the axis of rotation of the cylinder to which it is attached. In such a case complicated mechanisms and bearings have been required which permit the entire cylinder to be counter-skewed to correct for skew of the plate attached to it.